This invention relates to a process for the production of thiophenol compounds. Such compounds are well-known, having utility as anti-oxidants, polymerization inhibitors, intermediates for the preparation of other chemicals, etc.
Although the thiophenols have been known and used for many years, they remain costly and expensive chemicals. Numerous attempts to prepare these compounds have not resulted in an economical, pollution-free process.
For example, U.S. Pat. No. 2,490,257 discloses the vapor phase reaction of chlorobenzene and hydrogen sulfide in the presence of wood charcoal, while U.S. Pat. No. 3,799,989 teaches a non-catalytic process for preparing thiophenols from the same reactants. Other known methods of preparing thiophenols include the reaction between cyclohexane and sulfur or a sulfur chloride, as described in U.S. Pat. No. 3,671,593, and the reduction of phenylsulfonic acid chlorides with hydrazine.
Attempts to improve upon these prior art processes have recently been disclosed. Thus, U.S. Pat. No. 3,883,599 describes dehydrogenating the corresponding cyclohexylmercaptan by means of SO.sub.2 in the gaseous phase in the presence of an inert gas, with a dehydration catalyst. In U.S. Pat. No. 4,006,186, a process is described which comprises reacting a phenylsulfonic acid chloride with hydrazine hydriodic acid and hydrochloric acid to give the corresponding sulfonehydrazide, reacting the product so formed in a second step to provide the corresponding disulfide, reacting the latter material with hydrazine and alkali to form a thiophenolate, and subsequently liberating the thiophenol with a mineral acid.
However, all the prior art processes are subject to disadvantages in that they require costly multi-step methods or result in liberation of chlorine or hydrochloric acid, thus presenting pollution and environmental problems.